(a) Field of the Invention
The present invention relates to a schlieren optical device.
(b) Description of the Prior Art
When physical or chemical ununiform states in transparent gases, liquids and solids cause variations of refractive indices, a light passing therethrough is refracted and the ununiform states are observable as bright and dark shadows by use of a schlieren optical device.
The conventional schlieren optical device comprises, as shown in FIG. 1 for example, a pinhole 4 using as a spot light source 3 a light emitted from a light source 1 and focused by a condenser lens 2, a front (on the side of the light source) schlieren lens 5 for making the light emitted from the spot light source 3 into parallel rays, a rear (on the side of image) schlieren lens 7 for converging the parallel rays having passed through a sample 6, a knife edge 8 arranged at the rear focal point of the rear schlieren lens 7, an imaging lens 9 for forming an image of the sample, and a photographic means 10 consisting of a photographic film, a screen, etc. placed at the imaging position of the imaging lens 9. Used as the light source 1 is a tungsten lamp or halogen lamp, whereas a mechanical knife-shaped member is employed as the knife edge 8. The imaging lens adopts a single-group composition.
For experiments within a limited instrumentation space, for example, artificial earth satellite, a compact design and light weight are desired to reduce the cost for mounting the experimental device in the artificial earth satellite, low power consumption is demanded since a heavy-duty power source cannot be mounted in the artificial earth satellite, and high reliability is demanded so as not to allow experimental failure. Further, low calorific power is required since no convection is produced and cooling effect is low in the aerospace.
However, when the above-mentioned conventional schlieren optical device is to be used for observing a sample containing a portion having a large refractive index and great influence on optical path length such as the solution for growing crystal, it is very difficult to design a compact light-weight device for the reason described below. A first requisite for the compact design is to shorten the optical path length l as measured from the sample 6 to the photographing means 10 (FIG. 1). In the above-mentioned conventional example of the schlieren optical device wherein spherical aberration is corrected by the imaging lens 9 having the single-group composition, the above-mentioned optical path length ( must inevitably be long for correcting spherical aberration. Further, the white light source such as a tungsten lamp or halogen lamp used as the light source 1 in the conventional schlieren optical device produces remarkable chromatic aberration and makes it further difficult to design a compact and light-weight schlieren optical device. Furthermore, the conventional schlieren optical device using a tungsten lamp or halogen lamp as the light source 1 has a high calorific power and cannot be used in an enclosed space or vacuum condition such as aerospace free from convection.
Moreover, a tungsten lamp or halogen lamp has high power consumption and low reliability. In addition, the conventional schlieren optical device uses a mechanical knife-shaped member as the knife edge 8 and requires a mechanical retaining structure for retaining the knife edge. Therefore, the knife edge 8 may be mispositioned by vibration and/or high gravity produced by acceleration at the stage of launching a space ship and cannot assure high reliability for experiments in a space ship.